The following invention relates to an apparatus for locating the position of an object inside a body and more particularly to a medical system for locating the position of a feeding tube inserted into the stomach of a patient to verify its position and thus prevent injury to the patient.
Enteral feeding tubes are used in certain applications with patients who are incapable of feeding themselves by conventional means. These tubes are frequently inserted through the nasal cavity and then into the stomach for nasal gastric feeding. The distal end of such tubes is perforated to allow nutrients to be delivered to the proper location once the tube has been positioned. The tubes are typically 36-45 inches in length and require proper placement within the body to insure that the nutrients will be released at the correct location and to avoid damaging any tissue. Frequently, tube placement is verified by X-ray which requires that barium sulfate or some other radio opaque material be incorporated within the tube material. Also, reference markings on the tubes are used as general guidelines for the length of tube to be inserted for nasal gastric or transpyloric tube feeding.
The verification of tube placement is critical to safe use of these devices and the methods above have not always been satisfactory for this purpose. Tube markings are themselves only a rough approximation of the actual location of the end of the tube. Using X-rays to locate the tube brings the attendant problem of harm to the patient from repeated exposure to X-rays and the expense of a radiologist to administer them.
In the past, other solutions have been proposed and an example is shown in the U.S. patent to McCormick, U.S. Pat. No. 4,431,005. In the McCormick patent a feeding tube includes a piece of metal near the distal end of the tube which is detected by a probe that generates a small local magnetic field. The field is disturbed by the magnetically permeable metal in the tube and the sensitivity of the probe can be adjusted so that an alarm indication is provided when the probe is directly adjacent the metal inside the tube. This technique takes advantage of the fact that the magnetic field is not greatly affected by the biological tissue separating the probe from the metal in the tube. A problem with the aforementioned device, however, is that it may be difficult to find the distal end of the tube with the probe. The device emits a signal only when the probe is directly over the metal in the tubing and the tiny piece of metal may be difficult to locate as the tube is being inserted into the patient. There is no direction finding feature that tells the user when the probe is in the vicinity of the metal on the end of the tube but not yet exactly centered. The system is also highly susceptible to other metal objects which may be in the vicinity such as surgical instruments, needles and the like. Metal objects are commonly used in such situations and tend to confuse a probe which is, in essence, a metal detector.
What is needed, therefore, is a position verifying device which can locate an enteral feeding tube inside body tissue with a high degree of precision so that the position of the end of the tube within the body can be known.